The Coin's Edge discipline is a rarely practiced form of martial arts, one never taught at the Temple of Nine Swords, and thus never widely learned. The discipline was single-handedly created by a single swordsman, a legendary master known as Uther Doul. Doul had studied ancient tomes of an esoteric form of magic known as probability magic, a mystic practice that allowed its followers to alter the flow of probability and chance, bringing things that might have been into reality. Doul was able to create what he called probability meditations, mantras a warrior could use to similarly bend probability without having to have any mastery of magic. Doul used his probability meditations to great effect. He was able to call up possible strikes, extremely accurate or damaging attacks that could have been, and bring them into reality, and to do the reverse–to force foes to use only the weakest of attacks. He eventually developed a codified martial discipline, which he called the Coin's Edge school, relying on both these probability meditations and on a natural sense of chance, the gambler's intuition that is key to Coin's Edge maneuvers. The Coin's Edge discipline's associated skill is Profession (Gambler), as the ability to manipulate the odds to one's advantage is essential to the discipline. The associated weapons of the Coin's Edge discipline are the dagger, falchion, longsword, rapier, scimitar, and two-bladed sword.

Because the Coin's Edge discipline was never taught widely at the Temple of the Nine Swords or any similar center of training, most martial adepts do not know any maneuvers from it, or even know it exists. Only Swordsages can learn maneuvers from the Coin's Edge discipline. There are two ways to master the discipline. The first is to have been trained in it. If you choose to make a martial adept that has already been trained in the Coin's Edge discipline at character creation, you simply replace one discipline that adept could normally learn maneuvers from with the Coin's Edge discipline.

The other way is to seek out a master of the Coin's Edge discipline – a martial adept capable of using at least 5th – level maneuvers from the discipline–or one of the ancient texts of probability magic Uther Doul used, and to learn Coin's Edge from that source. You must train for a month under the master, or spend a month in research, and spend 1,000 xp at the end of your training. You gain the ability to learn maneuvers from the Coin's Edge discipline. In addition, you may exchange your maneuvers known for maneuvers of the Coin's Edge discipline. You may exchange one maneuver of each level, and the new maneuvers you learn must be of the same level as the exchanged maneuvers, unlike normal. The difficulty of finding an appropriate mentor or text is left to the DM to choose.